1. Field of the Invention
This invention relates to a structure of a speaker.
The present application claims priority from Japanese Application No. 2003-310468, the disclosure of which is incorporated herein by reference.
2. Description of the Related Art
A speaker as illustrated in FIG. 1 includes a voice coil bobbin 3 supported in such a way as to vibrate in an axis direction by a damper 2 placed between a frame 1 and the voice coil bobbin 3.
A voice coil 4 is wound on the outer periphery of the voice coil bobbin 3. A portion of the voice coil bobbin 3 on which the voice coil 4 is wound is inserted into a magnetic circuit gap g provided between a yoke 7 and a combination of a magnet 6 and a plate 5 forming a magnetic circuit, so that the voice coil bobbin 3 is vibrated in its axis direction (in the vertical direction in FIG. 1) by the magnetic circuit.
FIG. 1 also shows a speaker cone 8.
In the speaker structured in this manner, on the application of excessive input to the speaker, a lower portion of the voice coil bobbin 3 vibrating toward the rear of the speaker (vibration downward in FIG. 1) may come into collision with the yoke 7. This collision may damage the voice coil bobbin 3, which in turn may possibly make the speaker inoperable.
For this reason, in the conventional speakers as described above, a range a extending between a portion of the yoke 7, which opposes a rear end (the lower end in FIG. 1) of the voice coil bobbin 3, and a neutral position of the rear end of the voice coil bobbin 3 is longer than a range b extending between the plate 5 and a neutral position of a portion of the coupling between the voice coil bobbin 3 and the damper 2, in order to avoid collision of the voice coil bobbin 3 with the yoke 7 when excessive input is applied to the speaker.
Such a speaker is disclosed by Japanese Unexamined Patent Application No. 2003-116197, for example.
However, in consequence of such design for avoiding collision of a rear end of the voice coil bobbin 3 with the yoke 7, on the application of excessive input to the speaker, the coupling portion between the voice coil bobbin 3 and the damper 2 comes into collision with the plate 5 to cause a fracture in an adhesive A fixedly bonding the damper 2 and a speaker cone 8 to the voice coil bobbin 3. Hence, the conventional speakers as described above have the alternative problems of the speaker producing a defective sound output due to a malfunction in the voice coil, and abnormal sound being generated by the broken pieces of the adhesive A.